It is widely known that overuse of eyes through use of television, a computer, a portable terminal, and the like, which reduces blinking, and drying of air due to heating and cooling, which leads to evaporation of tears, cause dry eye symptoms. Dry eye is defined as a multifactorial disease of the tears and corneal surface that results in discomfort, visual disturbance, and tear layer instability with damage to the corneal surface (Non Patent Literature 1). An ophthalmic solution is often used for prevention, amelioration, and treatment of the dry eye symptoms. The tears may be classified into a tear aqueous layer containing water and mucin, and a tear lipid layer containing lipids and the like (Non Patent Literature 2). Basically, an approach to the tear aqueous layer is often adopted for prevention, amelioration, and treatment of the dry eye symptoms.
The approach to the tear aqueous layer has focus on the water in the tear aqueous layer, and is aimed at alleviation/amelioration of the dry eye symptoms by supplying water. This approach is a treatment method that has been heretofore widely performed as an artificial tear (Non Patent Literature 3). In addition, in recent years, there has also been known an approach with focus on the mucin in the tear aqueous layer, which is aimed at stabilizing the tear aqueous layer (uniform wetting and spreading of the tear aqueous layer over the corneal surface without rupture) by promoting mucin production. Drugs, such as Diquafosol and Rebamipide, having mucin production-promoting effects have been developed, and it has been reported that those drugs are used in dry eye treatment and have achieved high treatment effects (Non Patent Literature 4 and Non Patent Literature 5).
In recent years, it has been known that there are not a few cases of dry eye resulting from a reduction in secretion amount of the tear lipid layer due to, for example, Meibomian gland dysfunction or hypofunction (evaporative dry eye caused by Meibomian gland dysfunction) (Non Patent Literature 6). Normally, the tear lipid layer suppresses evaporation of the tear aqueous layer by covering a surface of the tear aqueous layer, to thereby prevent a dry eye condition. However, when the tear lipid layer is not secreted enough to be able to spread over the entirety of the tear aqueous layer, the tear aqueous layer cannot be protected, and hence the evaporation of the tear aqueous layer is accelerated, resulting in development of the dry eye symptoms. With regard to the evaporative dry eye, an investigation has been made into blending an oily component into an ophthalmic solution to supply the tear lipid layer from the ophthalmic solution (Patent Literature 1). As an evaluation method for an ophthalmic solution for, for example, prevention/treatment of evaporative dry eye symptoms caused by Meibomian gland dysfunction, there is known a measurement method for determining whether the tear aqueous layer and the tear lipid layer are separated into two layers (Non Patent Literature 7 and Non Patent Literature 8).
However, in development of eye drops for an evaporative dry eye application, in reality, a phenomenon in which the oily component in the eye drops is dispersed on the ocular surface, such as blurring of vision, occurs, and under the circumstances, even a dry eye treatment effect obtained by administering the eye drops containing the oily component is insufficient.
A polymer containing 2-methacryloyloxyethyl phosphorylcholine (MPC) (MPC polymer) is a polymer having extremely high hydrophilicity. The only known ophthalmological applications in which the MPC polymer is utilized are: an application as a contact lens lubricant for improving comfort of contact lens wear (Patent Literature 3); an application as an ophthalmic solution having blended therein the MPC polymer, for alleviating cytotoxicity (Patent Literature 2 and Non Patent Literature 9); and the like. No more novel applications have been provided.
As described above, under the circumstances, there has yet to be obtained a satisfactory ophthalmic solution for prevention, alleviation, amelioration, or treatment of evaporative dry eye symptoms caused by Meibomian gland dysfunction.